Heat controlled optoelectrical unit

ABSTRACT

The present invention relates to heat control and cooling of an optoelectrical unit, which converts between electrical and optical signal formats. The optoelectrical unit contains at least one optoelectrical capsule positioned on a circuit board. A primary heat sink is adapted to receive heat energy dissipated from the capsule. The capsule is oriented on the circuit board, such that it presents a relatively small footprint thereon and, at the same time, rises relatively large area sides, which do not face directly towards the circuit board. The primary heat sink has at least one cavity, which is adapted to the shape and dimensions of the capsule, such that the cavity contains at least one capsule. The primary heat couples thermally well to the capsule. Furthermore, the capsules assist in aligning the primary heat sink in its intended position.

FIELD OF THE INVENTION

The present invention relates generally to heat control and cooling ofoptical communication equipment. More particularly the invention relatesto an optoelectrical unit for converting information signals between anelectrical signal format and an optical signal format according to thepreamble of claim 1.

THE BACKGROUND OF THE INVENTION AND PRIOR ART

Optical communication systems transport information in the form ofmodulated light signals. A laser module, e.g. a semiconductor laser(laser=light amplification by stimulated emission of radiation) in asignal transmitter unit is here normally used in order to accomplish theoptical signals based on electrical ditto, and a photodetection module,e.g. a photodiode, in a signal receiver unit typically converts theoptical signals back into electrical signals again. In most cases, thesignal transmitter and a corresponding signal receiver are co-located toform an optoelectrical transceiver unit. These units, in turn, normallyoperate in an environment that includes one or more other units thatdissipate comparatively large amounts of heat energy, such that theambient temperature becomes fairly high. It is therefore particularlyimportant that the transceiver unit itself is efficiently cooled.

The above transmitter and receiver units should generally be as small aspossible with the aim of concentrating the number of processedinformation bits per physical volume unit and thereby reduce the overallsize of the optical communication equipment.

For the same reason, the transmitters and receivers should also beplaced as close as possible to each other. However, the photodetectionmodule and the laser module in particular produce a relatively largeamount of power losses in the form of heat energy, which must betransported away from the equipment in order to maintain an acceptableworking temperature. Normally, there are also restrictions as to theamount of heat energy that may be discharged from a particular unit inorder to guarantee that the temperature of any neighboring units stayswithin an acceptable range. Additionally, there may be a safetyincentive to limit the equipment's temperature so as to reduce the riskof burn injuries on the personnel that operate or service the equipment.

In the prior-art transceivers, the transmitter and receiver units aremost commonly placed in a respective indentation in the circuit board.Furthermore, the units are usually oriented with their largest side inparallel with the circuit board, such that they show a largest possibleinterface area towards a heat sink below and/or above the circuit board.

Classically, the heat power losses increase with increased processingspeeds/bitrates. A large amount of heat energy, in turn, requires arelatively large interface area towards a cooling medium in order to notresult in excessive equipment temperatures. Hence, increasing the ratioof processing capacity per volume or area unit implies a non-trivialoptimization problem.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide anoptoelectrical unit, which alleviates the problem above and thus offersa solution that is comparatively efficient with respect to theprocessing capacity per volume unit, and at the same time, enables anadequate dissipation of the heat power losses.

According to the invention the object is achieved by the initiallydescribed optoelectrical unit for converting information signals betweenan electrical and an optical signal format, which is characterized inthat the unit comprises at least two capsules which each of contains aparticular warmest side that radiates more heat energy than any one ofthe other sides of the respective capsule. Moreover, two of the at leasttwo the two capsules are positioned in relative proximity to each otheron the circuit board with their warmest sides substantiallyperpendicular to each other, such that the two capsules form a generalL-shape pattern on the circuit board.

This design is most advantageous, since it combines an efficient usageof the circuit board area with a competent cooling of the optoelectricalcapsules.

According to a preferred embodiment of the invention, the warmest sideof the capsule is one of the relatively large area sides. This designnamely improves the possibilities of accomplishing an efficient coolingvia, for example, an air cooled heat sink along the warmest side.

According to another preferred embodiment of the invention, the at leastone capsule has the general shape of a rectangular parallelepiped withtwo relatively large area sides and four relatively small area sides.Naturally, this does not imply that the capsule shape must represent amathematically perfect rectangular parallelepiped. On the contrary, itssides may be more or less tilted with respect to each other, such thatthey are either all pair wise parallel to each other or at least twoopposite sides being non-parallel to each other. For example, thecapsule may describe a truncated pyramid. Moreover, one or more of thecapsule's edges and/or corners may be rounded. In any case, the capsuleis positioned on the circuit board such that its relatively large areasides are oriented substantially perpendicular to a component side ofthe circuit board. An advantage accomplished by placing the capsule onits edge like this is that the capsule thereby not only shows arelatively small footprint on the circuit board, a relatively largecapsule area also becomes readily accessible for cooling by means of theprimary heat sink.

As mentioned initially, one capsule may contain a laser unit, whichreceives a first electrical information signal and produces in responsethereto a first optical information signal. Correspondingly, anothercapsule may contain a photodetection unit, which receives a secondoptical information signal and produces in response thereto a secondelectrical information signal.

According to a preferred embodiment of the invention, the primary heatsink has at least one coupling surface, which is adapted to the shapeand dimensions of the optoelectrical capsule. Specifically, this meansthat the coupling surface is substantially parallel and relativelyproximate to at least one side of the capsule. A good thermal couplingis thus accomplished between the capsule and the primary heat sink.

According to another preferred embodiment of the invention, theoptoelectrical unit includes at least one thermo conductive gap fillerbetween at least one optoelectrical capsule and at least one couplingsurface. The thermo conductive gap fillers are primarily intended toenhance the thermal coupling between the capsule and the primary heatsink by filling any air gap there between. The thermo conductive gapfillers are, however, also advantageous because they assist inaccomplishing a good mechanical fit between the capsule and the primaryheat sink.

According to yet another preferred embodiment of the invention, theprimary heat sink includes at least one cavity, which is adapted to theshape and dimensions of at least one of the capsules. The cavitycontains at least two cavity sides that are substantially parallel andrelatively proximate to at least two sides of the capsule. This isadvantageous, since the thermal coupling between the capsule and theprimary heat sink is thereby enhanced.

According to a further preferred embodiment of the invention, the twocavity sides above are substantially parallel and relatively proximateto two sides of each of the at least one capsule, which are alsomutually parallel to each other. In other words, the primary heat sinkat least partly surrounds the capsule. Naturally, this is preferable,since a comparatively large amount of heat energy from this capsule canthereby efficiently be absorbed by the heat sink. Moreover, the heatsink assists efficiently in holding the capsule in a fixed position onthe circuit board.

According to another preferred embodiment of the invention, the primaryheat sink is also adapted to receive heat energy, which is dissipatedfrom at least one circuit element on the circuit board in addition tothe least one capsule. Such combined heat sink function is advantageous,since it not only facilitates the assembly of the optoelectrical unit.Additionally, the total heat sink capacity is thereby utilized veryefficiently. Furthermore, during operation of the unit, the temperaturedistribution becomes more uniform across the unit. This is in turndesirable, since any mechanical stress on the unit resulting fromthermal expansion is thus reduced.

According to a further preferred embodiment of the invention, theprimary heat sink contains at least two surfaces, which aresubstantially parallel and relatively proximate to at least the warmestsides. This warrants for a good thermal coupling between the capsule andthe heat sink.

According to yet another preferred embodiment of the invention, theoptoelectrical unit comprises a secondary heat sink in addition to theprimary heat sink. The secondary heat sink is positioned such that itadjoins the primary heat sink. Heat energy may thereby be transportedbetween the primary heat sink and the secondary heat sink by means ofthermo conduction. This is advantageous, since the total heat sinkcapacity is thereby utilized very efficiently. Moreover it vouches for acomparatively uniform temperature distribution over the unit, which inturn is desirable, for instance from a mechanical stress point of view.

According to a further preferred embodiment of the invention, thesecondary heat sink contains an opening, which is adapted to the shapeand dimensions of the primary heat sink such that the secondary heatsink adjoins at least two sides of the primary heat sink. Hence, heatenergy may efficiently be transported between the two heat sinks.Preferably, the secondary heat sink completely surrounds the primaryheat sink, such that the primary heat sink and the secondary heat sinkform a joint outer surface of the optoelectrical unit.

According to a still further preferred embodiment of the invention, thesecondary heat sink is also adapted to receive heat energy from at leastone circuit element outside the coverage area of the primary heat sink.Thus, the heat sink arrangement's cooling capabilities become effectivefor other units than the optoelectrical capsules, which generally isdesirable. Preferably, a thermo conductive gap filler is includedbetween said at least one circuit element and the secondary heat sink.This namely both enhances the thermo conductive coupling there betweenand accomplishes a good mechanical fit between the capsule and the heatsink.

To sum up, the invention offers a highly efficient solution for coolingcommunication equipment in the form of optoelectrical units. Thereby thetemperature of these units, as well as any neighboring units, may bemaintained within a well-defined range. Naturally, the invention willtherefore provide a competitive edge to any communication system whereoptical transmitters are utilized for the transmission of information.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now to be explained more closely by means ofpreferred embodiments, which are disclosed as examples, and withreference to the attached drawings.

FIG. 1 shows a capsule containing a laser unit according to anembodiment of the present invention,

FIG. 2 shows a capsule containing a photodetection unit according to anembodiment of the present invention,

FIG. 3 shows an exploded diagram over a laser capsule according to anembodiment of the invention,

FIG. 4 depicts a circuit board according to an embodiment of theinvention, which comprises the capsules shown in FIGS. 1–3,

FIG. 5 a shows a bottom-view of a primary heat sink according to anembodiment of the invention,

FIG. 5 b shows a corresponding top-view of the primary heat sinkaccording to the embodiment shown in FIG. 5 a, and

FIG. 6 represents an exploded diagram over an entire optoelectrical unitaccording to an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Conventionally, the optoelectrical units (such as lasers andphotodetectors) in optoelectrical transceivers have been oriented withtheir largest side in parallel with the circuit board on which they aremounted. A largest possible interface area has thereby been accomplishedtowards at least one heat sink being placed either below, above or bothbelow and above the circuit board. This design, however, results in arelatively large footprint for each optoelectrical unit, which in turnconsumes valuable circuit board area that could have been used by otherunits. Therefore, the present invention proposes that the optoelectricalunits instead be placed on their edges, i.e. with a capsule side havinga comparatively small area towards the circuit board. FIG. 1 shows afirst example of this strategy, where a capsule 100 containing a laserunit stands on one of its relatively small area sides 101 d. The lasercapsule 100 is presumed to have the general shape of a rectangularparallelepiped with two relatively large area sides 101 a; 101 b andfour relatively small area sides 101 c, 101 d, 101 e and 101 f. Thelatter may either all have substantially the same size, or asillustrated in FIG. 1, have two somewhat larger sides 101 c; 101 d andtwo somewhat smaller sides 101 e; 101 f. Although the exact relationshipbetween the relatively large area sides 101 a; 101 b and the relativelysmall area sides 101 c–f is not critical for the proposed solution, therelatively large area sides 101 a; 101 b should preferably have at least50% larger area than the largest of the relatively small area sides 101c–f. It is furthermore advantageous, from an assembly point of view, ifthe capsule 100 is mounted such that the relatively large area sides 101a; 101 b are oriented substantially perpendicular to the circuit board.A feedthrough 102 in the bottom side 101 d of the capsule 100 containsone or more electrical leads 103 via which an incoming electrical signalE_(i) is received to the laser unit. Preferably, the electrical leads103 constitute ceramic conductors in the feedthrough 102 in order tomake possible a high lead density. The laser unit produces an outgoingoptical signal λ_(o) in response to the electrical signal E_(i) thatrepresents the same information. The optical signal λ_(o) is fed outfrom the capsule 100 to an optical fiber (not shown) via an opticalconnector 105, for example of LC-type (Lucent), SC-type (subscriberconnector) or MU-type (NTT). Here, the optical connector 105 is attachedto one of the relatively small area sides 101 e. Technically however, itmay equally well be attached to one of the relatively large area sides101 a or 101 b.

According to a preferred embodiment of the invention, one of therelatively large area sides 101 a radiates more heat energy than any oneof the other sides 101 b–101 f. I.e. this relatively large area side 101a is the warmest side of the capsule 100. For example, this may be dueto the fact that the laser unit is mounted on the inside of thisparticular side 101 a (see FIG. 3). Preferably, the capsule 100 alsocontains a thermoelectric module (such as a Peltier device), whichactively transports heat energy from the laser unit towards the side 101a of the capsule 100 exterior.

FIG. 2 shows a second example of a capsule 200 that contains anoptoelectrical unit according to an embodiment of the present invention.In analogy with the capsule 100 shown in FIG. 1 above, thephotodetection capsule 200 is presumed to have the general shape of arectangular parallelepiped with two relatively large area sides 201 a;201 b and four relatively small area sides 201 c, 201 d, 201 e and 201f. The photodetection capsule 200 is intended to stand on one of itsrelatively small area sides 201 d on a circuit board. As is apparentfrom the figure, the relatively small area sides 201 c–f all haveapproximately the same size. However, the relatively small area sides201 c–f may equally well have sizes, which are substantially differentin pairs, i.e. represent two somewhat larger sides and two somewhatsmaller sides. Although again, the exact relationship between therelatively large area sides 201 a; 201 b and the relatively small areasides 201 c–f is not critical for the proposed solution, the relativelylarge area sides 201 a; 201 b should preferably have at least 50% largerarea than the largest of the relatively small area sides 201 c–f. It isfurthermore advantageous, from an assembly point of view, if the capsule200 is mounted such that the relatively large area sides 201 a; 201 bare oriented substantially perpendicular to the circuit board.

According to a preferred embodiment of the invention, the capsule 200receives an incoming optical signal λ_(i) from, for example, an opticalfiber (not shown) via an optical connector 205 on one of the capsule's200 relatively large area sides 201 b. Preferably, if the opticalconnector 105 referred to above is attached to one of the relativelysmall area sides 101 c–f of the laser capsule 100, the optical connector205 should be attached to one of the relatively large area sides 201 aor 201 b of the photodetection capsule 200, and vice versa. The opticalconnector 205 may for instance be of LC-type (Lucent), SC-type(subscriber connector) or MU-type (NTT). The photodetection unit withinthe capsule 200 converts the optical signal λ_(i) into a correspondingelectrical signal E_(o) that represents the same information. Afeedthrough 202 in a bottom side 201 d of the capsule 200 contains oneor more electrical leads 203 via which the electrical signal E_(o) isdelivered to other circuit elements for further processing. Preferably,the electrical leads 203 constitute ceramic conductors in thefeedthrough 202 in order to make possible a high lead density.

According to a preferred embodiment of the invention, one of therelatively large area sides 201 a radiates more heat energy than any oneof the other sides 201 b–201 f and is thus the warmest side of thecapsule 200. For example, this may be due to the fact that thephotodetection unit is mounted on the inside of this particular side 201a. The capsule 200 may also contain a thermoelectric module (such as aPeltier device), which actively transports heat energy from thephotodetection unit towards the warmest side 201 a of the capsule 200exterior.

FIG. 3 shows an exploded diagram over a laser capsule 100 according toan embodiment of the invention. Here, an optoelectrical component in theform of a laser unit 310 is mounted on the inside of a side 101 a of thelaser capsule 100. A control circuitry 320 for the laser unit 310 is inturn positioned on top of this unit 310. Preferably, the capsule 100also contains a thermoelectric module (not shown), which activelytransports heat energy from the laser unit 310 towards the exterior ofthe capsule side 101 a. A capsule side 101 b in the form of a lid isused to seal the capsule 100 after assembly of the units therein.

FIG. 4 depicts a circuit board 400 according to an embodiment of theinvention, which comprises a laser capsule 100 and a photodetectioncapsule 200 as described above. Both these capsules 100 and 200 arepositioned on the circuit board 400 such that their relatively largearea sides 101 a, 101 b and 201 a, 201 b respectively are orientedsubstantially perpendicular to a component side of the circuit board400. For a given width D of the circuit board 400, this leaves arelatively large front space d_(f) that can be used for other purposesthan connecting optical fibers, for example displays (not shown) toindicate a transceiver status. Moreover, the distance d_(Δ) between theoptical connectors 105 and 205 can thereby be made comparatively short.

The capsules 100 and 200 are here presumed to have a respective warmestside 101 a and 201 a. Preferably, the capsules 100 and 200 arepositioned relatively close to each other with their warmest sides 101a; 201 a substantially perpendicular to each other, such that thecapsules 100 and 200 form a general L-shape pattern on the circuit board400. The circuit board 400 may also include a first circuit 430 and asecond circuit 440 in addition to the capsules 100 and 200, for instancefor pre- and post-processing of the electrical signals E_(i) and E_(o).

FIG. 5 a shows a bottom-view of a primary heat sink 500 according to anembodiment of the invention, which is to be placed on top of thecapsules 100 and 200 when mounted on a circuit board 400, as describedwith reference to FIG. 3 above. The primary heat sink 500 contains afirst cavity 510, which is adapted to the shape and dimensions of thelaser capsule 100 and a second cavity 520, which is adapted to the shapeand dimensions of the photodetection capsule 200. The cavities 510 and520 each contains a multitude of so-called coupling surfaces 510 a, 510b, 510 c and 510 f respective 520 a, 520 b, 520 c and 520 f. Thecoupling surfaces 510 a, 510 b, 510 c, 510 f, 520 a, 520 b, 520 c and520 f are cavity sides that are substantially parallel and relativelyproximate to the same number of sides of the respective capsule 100 and200 when the primary heat sink 400 is placed in its intended position. Agood thermal coupling is thereby accomplished between the capsules 100;200 and the primary heat sink 500.

According to a preferred embodiment of the invention, the primary heatsink 500 is designed such that it contains at least two surfaces, whichare substantially parallel and relatively proximate to at least saidwarmest sides 101 a and 201 a of the capsules 100 and 200. In FIG. 5 a,the cavity side 510 a of the first cavity 510 respective the cavity side520 a of the second cavity 520 represent these surfaces.

Preferably, the cavities 510 and 520 contain two cavity sides (couplingsurfaces) 510 a and 510 b respective 520 a and 520 b, which are mutuallyparallel to each other and that are substantially parallel andrelatively proximate to at least two sides 101 a, 101 b; 201 a, 201 b ofthe respective capsule 100 and 200 when the primary heat sink 500 isplaced in its intended position over the capsules 100 and 200. Thisensures a first-class thermal coupling between the capsules 100; 200 andthe primary heat sink 500. Furthermore, it accomplishes a goodmechanical fit between the capsules 100 and 200 and the primary heatsink 500, such that the capsules 100 and 200 assist in lining up theprimary heat sink 500 in its intended position. An efficient cooling ofthe capsules 100 and 200 is thus achieved, even in case one of thecapsules 100 and 200 (for some reason) is slightly misaligned from itsintended position.

According to another preferred embodiment of the invention, the primaryheat sink 500 is also designed such that it covers at least a part of atleast one of the first circuit element 430 and the second circuitelement 440 (see FIG. 6). The primary heat sink 500 is hence capable ofreceiving heat energy being dissipated from this(these) circuitelement(s).

A semi-transparent top-view of the primary heat sink 500 shown in FIG. 5a is illustrated in FIG. 5 b. The heat sink 500 preferably has planarinner surfaces and may, but need not, be equipped with radiating fins onits topmost outer surface.

FIG. 6 represents an exploded diagram over an entire opto-electricalunit according to an embodiment of the invention. The circuit board 400comprises a laser capsule 100, a photo-detection capsule 200 and threeother circuit elements 430, 440 and 450 respectively. The capsules 100and 200 and the first and second circuit elements 430; 440 arepositioned in accordance with what has been described with reference tothe FIGS. 4 and 5 a above.

A first thermo conductive gap filler, e.g. a thermo conductive pad,silicone or an equivalent gel 612 is attached on the top face and/or atleast one side face of the capsules 100 and 200 in order to enhance thethermal coupling between the relevant capsule(s) 100; 200 and theprimary heat sink 500. A corresponding second gap filler 610 is attachedto the warmest side of the laser capsule 100. Likewise, a third gapfiller 634 is attached on the upper surfaces of the first circuitelement 430 and the second circuit element 440.

The primary heat sink 500 is fitted onto the capsules 100 and 200 afterattaching the gap fillers 610, 612 and 634. Moreover, the first andsecond gap fillers 612 and 610 thereby removes any play between thecapsules 100; 200 the primary heat sink 500. The capsules 100 and 200thus assist in lining up the primary heat sink 500 in its intendedposition.

According to the illustrated embodiment of the invention, theoptoelectrical unit comprises a secondary heat sink 600, whichphysically adjoins the primary heat sink 500, such that heat energy maybe transported between the primary heat sink 500 and the secondary heatsink 600 by means of thermo conduction. Preferably, the secondary heatsink 600 contains an opening, which is adapted to the shape anddimensions of the primary heat sink 500 so as to adjoin at least twosides of the primary heat sink 500. For example, the secondary heat sink600 may completely surround the primary heat sink 500 (as shown in FIG.6) and hence accomplish an excellent thermal coupling between the units500 and 600. Furthermore, the heat sinks 500; 600 may be designed suchthat they form a joint outer surface of the optoelectrical unit. Roughlyspeaking, this means that the optoelectrical unit constitutes a sealedtight unit, which in turn, implies advantageous environmental attributesand provides a good electromagnetic compatibility (EMC) respectiveshielding against electromagnetic interference (EMI).

According to a preferred embodiment of the invention, the secondary heatsink 600 is adapted to receive heat energy from a third circuit element450 on the circuit board 400, which is positioned outside a coveragearea of the primary heat sink 500. A fourth thermo conductive gap filler635 is preferably attached on the upper surface of this circuit element450 in order to ensure a good thermal coupling also between the circuitelement 450 and the secondary heat sink 600. Naturally, the thirdcircuit element 450 may equally well be located on a different circuitboard than the circuit board 400, which contains e.g. the capsules 100;200 and any circuit elements 430; 440.

The term “comprises/comprising” when used in this specification is takento specify the presence of stated features, integers, steps orcomponents. However, the term does not preclude the presence or additionof one or more additional features, integers, steps or components orgroups thereof.

The invention is not restricted to the described embodiments in thefigures, but may be varied freely within the scope of the claims.

1. An optoelectrical unit for converting information signals between anelectrical signal format and an optical signal format, comprising: acircuit board which contains at least two optoelectrical capsules, theat least two capsules being positioned on the circuit board such thattheir respective footprint towards the circuit board has a smaller areathan the area of a largest side of the capsule, and a primary heat sinkadapted to receive heat energy being dissipated from at least one of theat least two optoelectrical capsules, wherein each of the at least twocapsules contains a particular warmest side radiating more heat energythan any one of the other sides of the respective capsule, and two ofthe at least two capsules are positioned in relative proximity to eachother on the circuit board with their warmest sides substantiallyperpendicular to each other such that the two capsules form a generalL-shape pattern on the circuit board.
 2. An optoelectrical unitaccording to claim 1, wherein the warmest side is one of the relativelylarge area sides.
 3. An optoelectrical unit according to claim 1,wherein each of the at least two capsules has the general shape of arectangular parallelepiped with two relatively large area sides and fourrelatively small area sides, and the at least two capsules arepositioned on the circuit board such that their relatively large areasides are oriented substantially perpendicular to a component side ofthe circuit board.
 4. An optoelectrical unit according to claim 3,wherein the primary heat sink comprises at least one coupling surfaceadapted to the shape and dimensions of at least one of the at least twooptoelectrical capsules such the at least one coupling surface issubstantially parallel with and relatively proximate to at least oneside of said at least two capsules.
 5. An optoelectrical unit accordingto claim 4, wherein the unit comprises at least one thermo conductivegap filler between at least one of the at least two optoelectricalcapsules and at least one of the at least one coupling surface.
 6. Anoptoelectrical unit according to claim 4, wherein the primary heat sinkcomprises at least one cavity adapted to the shape and dimensions of atleast one of the at least two capsules such that the at least one cavitycontains at least two cavity sides being substantially parallel with andrelatively proximate to at least two sides of at least one of the atleast two capsules.
 7. An optoelectrical unit according to claim 6,wherein the at least two cavity sides are substantially parallel withand relatively proximate to at least two mutually parallel sides of atleast one of the least two capsules.
 8. An optoelectrical unit accordingto claim 1, wherein the primary heat sink is adapted to receive heatenergy being dissipated from at least one circuit element on the circuitboard in addition to the least two capsules.
 9. An optoelectrical unitaccording to claim 1, wherein the primary heat sink contains at leasttwo surfaces being substantially parallel and relatively proximate to atleast said warmest sides.
 10. An optoelectrical unit according to claim1, wherein the unit comprises a secondary heat sink adjoining theprimary heat sink such that heat energy may be transported between theprimary heat sink and the secondary heat sink by means of thermoconduction.
 11. An optoelectrical unit according to claim 10, whereinthe secondary heat sink contains an opening adapted to the shape anddimensions of the primary heat sink such that the secondary heat sinkadjoins at least two sides of the primary heat sink.
 12. Anoptoelectrical unit according to claim 11, wherein the secondary heatsink surrounds the primary heat sink and that said heat sinks form ajoint outer surface of the optoelectrical unit.
 13. An optoelectricalunit according to claim 10, wherein the secondary heat sink is adaptedto receive heat energy being dissipated from at least one circuitelement outside a coverage area of the primary heat sink.
 14. Anoptoelectrical unit according to claim 1, wherein at least one of the atleast two capsules contains a laser unit receiving a first electricalinformation signal and producing in response thereto a first opticalinformation signal.
 15. An optoelectrical unit according to claim 1,wherein at least one of the at least two capsules contains aphotodetection unit receiving a second optical information signal andproducing in response thereto a second electrical information signal.16. An optoelectrical unit according to claim 1, wherein at least one ofthe at least two capsules contains a thermoelectric module activelytransporting heat energy from an optoelectrical component inside thecapsule towards the exterior of the capsule.
 17. An optoelectrical unitaccording to claim 16, wherein the thermoelectric module includes aPeltier device.